Computer numerical control machine tools such routers used in the woodworking, plastics nonferrous metal industries, typically consist of a base unit, a stationary or movable workpiece support table mounted on a base unit, a stationery or movable gantry mounted on or adjacent the base unit, and a toolhead assembly mounted on a transversely disposed bridge member of the gantry. Either the table or the gantry is displaceable relative to the base unit longitudinally or along an x-axis, the toolhead assembly is displaceable transversely or along a y-axis and the tool is displaceable vertically or along a z-axis. The table or gantry, the toolhead assembly and the tool are displaced along their respective axes by feedscrews driven by servomotors. The motions of the various components of the machine are controlled by a controller which operates the various servomotors of the machine according to instructions of a program inputted into the controller.
Workpieces to be machined are positioned on the table of the machine and located in predetermined locations by the use of pop-up pins provided on the table or other means, and are held down by various means including clamps and vacuum systems. Vacuum systems may consist of conventional systems which are suitable for large production runs, and universal systems which are more suitable for short production runs. A conventional vacuum system generally includes a vacuum port provided in the workpiece table, connected to a vacuum pump and a vacuum fixture positioned on the workpiece table about the vacuum port on which the workpiece is positioned. The fixture is provided with a peripheral rubber seal engaged by the workpiece seated thereon, which permits the evacuation of air between the fixture and the workpiece to hold the workpiece in place. A universal vacuum system generally includes a table having a lower rigid plate, an intermediate plate having a recessed upper surface arranged in a grid pattern, an upper spoilboard formed of a porous material such as particleboard, closing the recessed grid pattern in the intermediate board to form a plenum and vacuum pump operatively connected to the plenum. As a vacuum is applied to the plenum, air is drawn through the particleboard to produce a low pressure zone at the surface of the particleboard, which functions to hold a workpiece positioned on the particleboard.
Although both conventional and universal vacuum systems of the type described have been effective in holding down workpieces in both long and short production runs, they have several disadvantages. They either require special vacuum fixtures as in the instance of conventional vacuum systems or require a large amount of airflow to remove the air drawn through the particleboard of universal systems. It thus has been desirable to provide an improved vacuum system for holding down workpieces positioned on the table of a machine tool of the type described which will provide greater versatility in positioning workpieces on the table and which will not require a high volume of airflow to provide a vacuum sufficient to effectively hold down workpieces to be machined.